1. Field
The present invention relates generally to a method of forming a mold for a fiberglass reinforced plastic (FRP) swimming pool, spa, or pond, and specifically to a method for providing a rapid process for mold development.
2. Description of the Related Art
The desire to create artificial bodies of recreational water for swimming or landscape aesthetics has been around for centuries. The general concept of building a vessel in or above ground that can be used for swimming and other water sports has been a part of nearly every recorded society. There are three basic categories of swimming pool construction methods. The oldest and largest method involves forming a concrete shell in an excavated hole. The concrete maybe be poured as a monolithic slab, sprayed onto a reinforcing steel cage using a “shotcrete” method, or can be hand packed. This concrete is in turn made water tight through a plaster or other surface coating. Alternatively, a hole can be excavated and polymer, steel, or wood walls installed along with a vinyl membrane, which lines the interior surface of the entire pool. Finally, the most recent construction method involves producing a FRP pool shell, which is transported to the excavated site by truck and placed in the hole in one pieced. It is the latter method of pool shell construction that this invention concentrates. While the process described further will concentrate on a method to produce a pool shell it is understood that this process could be expanded easily to spas, ponds, and other containment vessels.
In creating an FRP pool, spa, or pond shell one must first build a model, or plug, from which the mold is constructed. The mold is simply a mirror image of the pool. Release agents are placed on the mold and the pool or spa shell is constructed out of layers of fiberglass material and once cured, the entire shell is released from the mold. Construction of the mold is the critical and costly step in building FRP pools. Because the mold has to be structurally rigid to maintain its shape, it requires significant reinforcing substructure. As well, the original pool design has to be translated from a three dimensional computer or hand drawing into an actual mold. In many objects, such as a large boat hull, recreational vehicle decorative shell, or a car/truck body, it is fairly easy to construct a positive model, commonly referred to as a plug, so that a negative (mirror image) mold can be constructed from the plug. This allows the advantage of seeing the final part and fine tuning it before the mold is actually constructed. Once the mold is created a master plug, called a glass master, can be constructed so that many duplicate molds can be created. Like the mold, the glass master has a lot of structural reinforcement material in order to retain its precise shape. This is compounded when building extremely large parts such as what are found in swimming pool shells.
In the case of constructing a swimming pool plug, it is often difficult to build a positive part, because the actual pool is a “negative” space. In other words, it is difficult to build a model of a hole. For this reason swimming pool molds are typically fashioned in one of two methods. The first method involves building a temporary mold, which visually is an inside out swimming pool. This necessitates detailed drawings and exact measurements. It can be constructed from combinations of wood, fiberglass, plaster, auto repair putty, or the like, and once the rough shape is achieved the entire temporary mold is sprayed with a tooling gel coat and waxed. At this point, a highly reinforced pool, the glass master, is constructed. This glass master is stored for later reproduction of the mold. The disadvantages of this method are numerous. It requires many hours of sanding and filling in order to create the smooth finish of the original temporary mold. The temporary mold itself is made from a wide range of materials with different thermal expansion coefficients and different thermal conductivity coefficients, which result in an uneven cure on the glass master. This can lead to stress fractures and other imperfections due to shrinkage the glass master, especially over time. Equally important, is that one does not get a good visual view of what the pool will look like until after the glass master is constructed. This is well after most of the expense in producing the tooling has occurred. This can lead to designs that are not ideal and further work on the glass master to correct these design flaws can compound the problem of deterioration of the glass master surface and reduce the ultimate longevity of the mold.
In the second common method, various pieces of FRP pool shells can be spliced together to form a positive plug that can be viewed. This requires an inventory of steps, walls, and swim-outs, and these are then tied together with the same materials used above: wood, fiberglass, plaster, auto repair putty, or the like. Once this structure is completed it is coated with a tooling gel coat and release and a mold is built inside this plug. In this case the mold can suffer because of the non-uniform curing that occurs due to the various materials used in construction and the wide range of different thermal expansion coefficients and different thermal conductivity. These areas of higher and lower cure, and higher and lower shrinkage during cure, can result in stress fractures and warping that limit the life of the tool. The corrective action is to once again build a glass master on the mold before it is used so that the mold can be replaced when it eventually deteriorates, which results in more cost and labor. A further disadvantage is that all of the pool shells tend to look alike, because they are fashioned from many of the same subparts. Also, the lines of the pool tend to be simple, because it takes much more time, labor, and materials to create more complex geometries.
Finally, FRP pool shells produced on any mold often require detailing or minor repairs due to mold imperfections, transportation, or installation damage. During repair of these FRP pool shells it may be difficult or impossible to match the exact surface finish of the pool shell. This is typically caused by the mold sealer or wax filling in the micro porosity of the surface giving it an extremely shiny and reflective surface. While this surface characteristic is desirable on boats, cars, and other FRP products, it is not necessary on a pool, spa or pond, because the surface will be underwater. Below the surface, the water masks this surface finish. It is desirable for the surface to have a matte finish so that repairs can be easily accomplished with out going thorough a sequence of higher and higher sandpaper grits followed by buffing. In addition to the mold release masking the matte finish on the finished part, the matte finish on the mold also causes difficulty in separating the part from the mold, further complicating the production.
Various patents have been proposed to make molds for both cementitious products and fiberglass parts. Examples include U.S. Pat. Nos. 4,948,296; 2,910,759 to Lifter et al.; 4,060,946 to Lang et al.; 4,074,481 to Lang et al.; 4,090,266 to Price; 4,015,379 to Colson, Jr.; 6,637,162 B1 to Holland. However, none of these overcome the problems associated with the manufacturing of large one-piece fiberglass pool molds and none address the dramatic reduction of cost and performance benefits realized by the invention described here.